A semiconductor designed for, for example, converting and controlling power such as an inverter system is referred to as a power semiconductor. A power semiconductor for controlling a high voltage and a large current is desired to be capable of using a large power efficiently. For this reason, the power semiconductor needs to maintain a leak current without breaking even when an extremely high voltage is applied. A maximum applicable voltage is referred to as a resisting pressure.
For example, a motor that is used for a household air conditioner outputs a power of 1 kW. For this reason, a power semiconductor for use in an air conditioner needs to be resistant against, for example, a voltage of 100 V or above and a current of 10 A. Furthermore, a power semiconductor switching element needs to minimize power loss on a path in order to control a current path. For this reason, the ON resistance of the power semiconductor switching element needs to be minimum.
There are various kinds of power semiconductor switching elements such as a switching element using an insulation gate bipolar transistor (IGBT) and a switching element using SiC. Among this, a field-effect transistor (FET) using a nitride semiconductor (for example, a nitride gallium (GaN)) has been actively researched and developed as a next-generation element (for example, refer to Non-patent Literature 1).
The power semiconductor switching element such as an FET has a source terminal, a drain terminal, and a gate terminal. A resistance between the drain and source terminals is controlled by a voltage to be applied to the gate terminal. When a gate voltage reaches or exceeds an ON voltage (Vth), the line between the drain and source is switched from OFF (insulated) to ON (short-circuited).